1. Field of the Invention
The present invention relates to a mold for manufacturing a metal-ceramic composite member in which a ceramic and a metal are firmly joined together by a direct joining strength on an interface therebetween.
2. Description of the Related Art
Metal-ceramic composite members taking advantages of characteristics of ceramic such as chemical stability, high melting point, insulation performance, high hardness, and relatively high heat conductivity and characteristics of metal such as high strength, high toughness, easy workability, and electrical conductivity are in wide use for automobiles, electronic equipment, and so on, and typical examples thereof are metal-ceramic composite substrates and packages for automobile turbocharger rotors and for mounting high-power electronic elements.
As methods for manufacturing the metal-ceramic composite members, adhesive bonding, plating, metallization, thermal spraying, enveloped casting, brazing and soldering, and a DBC method are well known in the art, and most of the metal-ceramic composite members have recently been manufactured by the DBC method using alumina substrates and a metal active brazing method using aluminum nitride substrates in view of cost problem.
This applicant previously proposed “MANUFACTURE OF METAL-CERAMIC COMPLEX MEMBER, MANUFACTURING APPARATUS AND MOLD FOR MANUFACTURING” in Patent document 1 as a method, apparatus, and mold for directly joining aluminum as a metal plate onto a ceramic member such as a ceramic substrate.
A manufacturing apparatus according to this proposal includes: an atmosphere replacing part where an atmosphere in a mold in which a ceramic member is vertically held is replaced with an atmosphere whose oxygen concentration is controlled at a predetermined value or lower; a preheating part where the mold is preheated; a molten metal pouring part where a molten metal is poured into the mold while the temperature in the mold is maintained at a pouring temperature; a cooling/joining part where the temperature in the mold is lowered to a joining temperature at which the molten metal starts solidifying to join a metal onto a surface of the ceramic member; and a slow cooling part where the mold is cooled slowly. As a result, the use of these manufacturing apparatus and mold makes it possible to make a metal-ceramic joining strength firm, and, moreover, even when metal plates different in thickness are joined onto both faces, metal plates with high precision and uniform thickness can be easily joined if the precision of the mold is controlled to be appropriate.
After the above proposal was made, in accordance with the expansion of the market for metal-ceramic composite members, there has been an increasing demand for the supply of metal-ceramic composite members in various shapes at low cost. In particular, a power amount dealt by the metal-ceramic composite member has been increased, and in accordance with this increase, new demands have arisen for larger and thicker metal plates and more complicated shape thereof for the purpose of dealing with generated heat and for other purposes. There are some cases, however, where the aforesaid proposal cannot always fully respond to such demands.
For example, when a metal-ceramic composite member in which a plurality of ceramic substrates are joined onto a large joining metal is to be produced through the use a mold according to Patent document 1, the ceramic substrate in the mold becomes unsupported due to buoyancy of a poured molten metal, so that stability in shape of the manufactured metal-ceramic composite member cannot be maintained.
Therefore, the inventors of the present invention have made such a proposal in Patent document 2 that a ceramic substrate is placed in a crucible, utilizing its own weight, with a face thereof to be in contact with a molten metal facing upward and the molten metal is poured from above. As a result, it was made possible to manufacture a metal-ceramic composite member in which a plurality of ceramic substrates are joined onto a large joining metal.
(Patent Document 1)
Japanese Patent Laid-open No. Hei 11-226717
(Patent Document 2)
Japanese Patent Laid-open No. 2002-76551
In recent years, a demand for a larger metal as a metal to be joined onto a ceramic substrate has been increasing in accordance with the expansion of the intended use of metal-ceramic composite members, whereas a demand for dimensional precision has been also increasing. In the proposal of Patent document 2, however, a large number of swells occur on a free surface of a large joining metal after the solidification, and in addition, dimension control of the large joining metal is difficult. Consequently, it is necessary to provide a step of polishing the joining metal after a step of joining the joining metal and the ceramic substrate together, which has been explained hitherto, for the purpose of swell removal and dimension control. This has been a factor of lowering productivity and increasing cost. Therefore, an object of the present invention to solve the problem is to provide a mold that is capable of manufacturing, in the aforesaid joining step, a metal-ceramic composite member having a large joining metal free from swell and high in dimensional precision.
Further, the proposal of Patent document 2 adopts such a structure that a ceramic substrate is placed horizontally and a metal is joined only onto one face, and therefore, it is not possible to join the metals on both faces concurrently.